Mirror mounting structures and methods for scanners employing limited rotation motors

ABSTRACT

A scanning assembly is disclosed for providing controlled movement of a mirror. The scanning assembly includes a motor shaft of a limited rotation motor, a scanning device, and a scanning device mounting unit. The mirror mounting unit includes a tapered base for coupling the scanning device mounting unit to the output shaft of the limited rotation motor. One of the tapered base and the output shaft includes a cylindrical tapered male plug having a decreasing inner diameter that decreases along a direction of coupling of the tapered base and the output shaft for engaging the tapered base to the output shaft. The tapered base includes an overall taper angle of at most about 4.0 degrees from the rotational axis of the output shaft.

PRIORITY

The present application is a continuation application of U.S. patentapplication Ser. No. 10/996,524 filed on Nov. 23, 2004, which claimspriority to U.S. Provisional Patent Application Ser. No. 60/524,683filed Nov. 24, 2003.

BACKGROUND

The invention relates to limited rotation motors such as galvanometers,and particularly relates to limited rotation motors used to driveoptical elements such as mirrors for the purpose of guiding light beamsin scanners.

Limited rotation motors generally include stepper motors and constantvelocity motors. Certain stepper motors are well suited for applicationsrequiring high speed and high duty cycle sawtooth scanning at large scanangles. For example, U.S. Pat. No. 6,275,319 discloses an opticalscanning device for raster scanning applications.

Limited rotation motors for certain applications, however, require therotor to move between two positions with a precise and constant velocityrather than by stepping and settling in a sawtooth fashion. Suchapplications require that the time needed to reach the constant velocitybe as short as possible and that the amount of error in the achievedvelocity be as small as possible. Constant velocity motors generallyprovide a higher torque constant and typically include a rotor and drivecircuitry for causing the rotor to rotate about a central axis, as wellas a position transducer, e.g., a tachometer or a position sensor, and afeedback circuit coupled to the transducer that permits the rotor to bedriven by the drive circuitry responsive to an input signal and afeedback signal. For example, U.S. Pat. No. 5,424,632 discloses aconventional two-pole limited rotation motor.

A requirement of a desired limited rotation motor for certainapplications is a system that is capable of changing the angularposition of a load such as a mirror from angle A to angle B, with anglesA and B both within the range of angular motion of the scanner, and bothdefined arbitrarily precisely, in an arbitrarily short time whilemaintaining a desired linearity of velocity within an arbitrarily smallerror. Both the minimum time of response of this system and the minimumvelocity error are dominated by the effective bandwidth of the system.The bandwidth of the system is the concatenation of the servo amplifierbandwidth with that of the scanner.

For example, such limited rotation motors may be used in a variety oflaser scanning applications, such as high speed surface metrology.Further laser processing applications include laser welding (for examplehigh speed spot welding), surface treatment, cutting, drilling, marking,trimming, laser repair, rapid prototyping, forming microstructures, orforming dense arrays of nanostructures on various materials.

The processing speeds of such systems are typically limited by one ofmore of mirror speed, X-Y stage speed, material interaction and materialthermal time constants, the layout of target material and regions to beprocessed, and software performance. Generally, in applications whereone or more mirror speed, position accuracy, and settling time arefactors which limit performance, any significant improvement in scanningsystem bandwidth may translate into immediate throughput improvements.

There is a need, therefore, for an improved limited rotation motorsystem, and more particularly, there is a need for a rotor for a limitedrotation motor that provides improved bandwidth.

SUMMARY

The invention provides a scanning assembly for providing controlledmovement of a mirror. The scanning assembly includes a motor shaft of alimited rotation motor, a scanning device, and a scanning devicemounting unit. The mirror mounting unit includes a tapered base forcoupling the scanning device mounting unit to the output shaft of thelimited rotation motor. One of the tapered base and the output shaftincludes a cylindrical tapered male plug having a decreasing innerdiameter that decreases along a direction of coupling of the taperedbase and the output shaft for engaging the tapered base to the outputshaft. The tapered base includes an overall taper angle of at most about4.0 degrees from the rotational axis of the output shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description may be further understood with reference tothe accompanying drawings in which:

FIG. 1 shows an illustrative diagrammatic view of a mirror and rotorassembly for a limited rotation motor system in accordance with anembodiment of the invention;

FIG. 2 shows an illustrative diagrammatic side sectional view of themirror and rotor assembly shown in FIG. 1 taken along line 2-2 thereof;

FIG. 3 shows a portion of the illustrative diagrammatic side sectionview of FIG. 2 on an enlarged scale;

FIG. 4 shows a portion of a side sectional view similar to that shown inFIG. 3 of a mirror and rotor assembly for use in a limited rotationmotor system in accordance with a further embodiment of the invention;

FIG. 5 shows an illustrative isometric view of a mirror mountingstructure for use in a limited rotation motor system in accordance withan embodiment of the invention;

FIG. 6 shows an illustrative isometric view of a unitary mountingstructure and mirror for use in a limited rotation motor system inaccordance with another embodiment of the invention;

FIGS. 7 shows an illustrative diagrammatic isometric view of a limitedrotation motor system in accordance with an embodiment of the invention;and

FIGS. 8 and 9 show illustrative diagrammatic side sectional views offurther limited rotation motor systems of further embodiments of theinvention.

The drawings are shown for illustrative purposes only.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Optical scanning applications typically require that a mirror beattached to a shaft of a motor either directly or indirectly. Forexample, clamp-like parts have been employed that function to supportthe mirror as well as to attach it to the shaft. Inseparablecradle-and-clamp designs that are built into or onto the mirror havealso been employed. Sometimes the mirror is simply cemented into atransverse slot in the shaft.

Applicant has discovered that providing an improved mirror mountingstructure may provide limited rotation motor systems with improvedbandwidth. In the general case, it is desirable that the mirror beattached in a way that permits easy assembly and/or removal. This isnecessary to ease system assembly and alignment, and also to accommodatereplacement of the mirror with one of a different size or reflectivityrange, or to allow replacement of a damaged mirror in situ. Of course,it is also the function of the mounting means to assure geometricalalignment of the mirror as mounted to the shaft, at least in thedirection normal to the mirror surface. Lastly, it is of greatconsequence that the inertia of the mount itself not compromise theperformance of the system in dynamic applications, and be robust inproportion to the shock and vibration environment of static systems.

As shown in FIGS. 1 and 2, a minor mounting structure 10 in accordancewith an embodiment of the invention includes a transverse slot intowhich a mirror may be cemented, soldered or otherwise fastened, and atapered base 18 that may be received within a tapered opening 16 in arotor output shaft 14. The transverse slot is formed by slot elements 20and 22 as shown in FIG. 2. The mirror mounting structure 10 retains thesimplicity of having a transverse slot in the shaft, but is replaceable,attaches securely yet adds little or no inertia to the system, supportsthe mirror in proportion to its size, and allows a high degree ofaccuracy in geometrical mirror alignment. The mirror mounting structure10 is also shown on an enlarged scale in FIG. 5. As shown in FIG. 5, thebase 18 includes a taper angle as indicated at 19. The structure 10 mayalso include a small hole 24 on one or both sides through which one ortwo rotation stops 25 a, 25 b may be placed in certain embodiments. Therotation stops 25 a and 25 b may be formed by two ends of a single pinthat passes through the structure 10, or may be formed as two separatestops. The taper may be linear as shown in FIG. 5, or in furtherembodiments the taper may be non-linear. The use of a tapered mirrormount may provide improvement in efficiency of about 25 percent to about35 percent.

As shown in FIG. 4, in accordance with another embodiment of theinvention, a mirror mounting structure 30 may include a tapered openingin its base 38 that receives a tapered end 36 of a rotor output shaft34. The structure 30 also includes a transverse slot into which a mirror32 is cemented, soldered or otherwise secured. In each embodiment, themirror end of the coupling unit is of a diameter, and therefore thelength of the sides of the slot supporting the mirror are of a length,proportionate to the supporting rigidity, required for that particularmirror size and design. The mirror end of the coupling unit may bemodified from a cylindrical form into an ellipse or other shape asrequired to provide a desired length of support for the mirror. Thedepth of the slot may also be adjusted as appropriate. The unit istapered on the exterior at an angle, and has such a length, that it isself-locking against the motor maximum torque in the most generalembodiment.

Different applications may require different degrees of locking. Forexample, it might be desired that the direction perpendicular to theface of the mirror be hand-re-adjustable with respect to the angularposition of the shaft during assembly and alignment of the opticalsystem of which it is a part. This application would result in arelatively large taper angle. On the other hand, it might be that theoptical system of which it is a part must withstand large accelerations,such as those during launch of a space vehicle. This application wouldrequire a relatively small taper angle.

The angle of taper and length of engagement are chosen over a range ofangles and lengths as a compromise between the need for a self-lockingfit, and the desire for easy release when required. The general range ofuseful angles for locking is between 0.03 and 0.07 inches per inch.Tapers at the smaller-taper end of the range tend to grip very tightly,and at the upper end to release easily. It is also within the scope ofthe invention to design the taper angle and engagement length so thatthe tapers lock so tightly as to become essentially permanently affixed,and, conversely, to release so easily that they must be bonded togetherto transmit meaningful torque.

In order to maximize the stiffness and minimize the inertia of theassembly, the plug and recess preferably occupy volume inside thebearing that supports the output. It is, however, within the scope ofthe invention that the unit and it's mating shaft portion be positionedanywhere along the shaft axis.

The end of the shaft or post is equipped with a concentric hollow recessin the embodiment of FIG. 3 in the form of a mating taper, so that whenthe base 18 in the form of a male plug is inserted into the recess andforced together into position, the tapers lock. Such a joint has optimumperformance in terms of concentricity, lack of tilt, torquetransmission, and freedom from a tendency to loosen in use. When it isdesired to remove the mount, a plier-like tool may be clamped to theflats on the plug, and an axial tensile force of a few pounds, dependingon the size of the mount and the design of the taper, is applied betweenthe plier and the inner ling of the front bearing, in the case of amotor, or galvanometer, or a suitable flange in the case of a mountingpost (not shown), thus releasing the taper without damage.

As shown in FIG. 6, a system in accordance with another embodiment ofthe invention may include a unitary minor and mounting unit 26 with apolished surface 27 (that provides a mirror) and a base 28 having ataper as indicated at 29.

As shown in FIG. 7, a scanner assembly including a rotor shaft andmirror mounting structure in accordance with an embodiment of theinvention may include a scanner motor 40, having a rotatable rotor withan outer shaft 48 as discussed above, with transducer 42 for monitoringthe position of the shaft attached to one end of the rotor and ascanning element 44, which may comprise a mirror, attached to the outputshaft of the scanner motor 40 at an opposite end from the positiontransducer. Of course, the scanning element 44 and the positiontransducer 42 may each be attached to the rotor at the same end thereof.The system also includes a feedback control system 46 that is coupled tothe transducer 42 and the motor 40 as shown to control the speed and/orposition of the motor.

As shown in FIG. 8, a mirror mounting structure in accordance with anembodiment of the invention may be used with in a system 50 thatincludes a backiron 52, stator coils 54 and a magnet 56 that is securedto a shaft 58. The shaft 58 is rotatably mounted to a housing structure(not shown) via bearings 64. A scanner element such as a mirror 60 ismounted to one end of the shaft 58 while a position transducer 62 ismounted to the other end of the shaft 58.

As shown in FIG. 9, a limited rotation torque motor assembly 70 inaccordance with a further embodiment of the invention may include abackiron 72, stator coils 74 and a magnet 76 that is secured to a shaft78 as discussed above. A mirror 80 is attached to the shaft via a mirrormounting structure of the invention and the shaft is rotatably securedto a housing structure (not shown) via bearings 84. The assembly 70 mayfurther include a position transducer as discussed above.

For example, such limited rotation motors may be used in a laserdrilling system for producing vias (or holes) in printed circuit boards(PCBs). The system may include a pair of galvanometer based X-Y scannersas well as an X-Y stage for transporting the PCB, and a scan lens thatprovides for parallel processing of circuit board regions within thefield covered by the scanners and lens. The X-Y stage transports thecircuit board along rows and columns needed for entire coverage. Thecircuit board is typically substantially larger than the scan field.

Such limited rotation motors may also be used in multi-layer drillingsystems in accordance with another embodiment of the invention. Theoperations may include hole punching (or percussion drilling) where oneor more laser pulses form a single hole within an effective spotdiameter without relative movement of the beam with respect to object,or may include trepanning (which does involve relative movement betweenthe beam and the object during the drilling operation). Duringtrepanning, a hole having a diameter substantially larger than a spotdiameter is formed. A substrate is laser drilled from a top surface ofthe substrate to an exposed bottom surface of the substrate using aplurality of laser pulses that are preferably trepanned in a circle, butother trepanning patterns, such as ovals and squares, may be used. Forexample, a trepanning pattern of movement of the laser focal spot is onein which the beam spot starts in the center of the desired via, andgradually spirals outwardly to an outer diameter of the via. At thatpoint the beam is caused to orbit around the via center for as manyrevolutions as is determined necessary for the particular via. Uponcompletion, the focal spot is caused to spiral back to the center andthereafter awaits the next command. An example of a trepanning velocityis 3 millimeters per second. In such drilling applications, it issometimes advantageous to provide rapid point to point positioning ofthe beam with a rapid settling time irrespective of the trajectorybetween the points.

The overall drilling system throughput can be affected by many factorssuch as the required number of holes within a field, hole size, stagespeed, etc. System bandwidth improvements may be generally useful withina substrate drilling system, and such improvements may be particularlyadvantageous in substrate drilling systems wherein trepanning or similarmotion is used for hole formation. Limited rotation motors discussedabove may also be employed for drilling other substrates such aselectronic packages, semiconductor substrates, and similar workpieces.

Such limited rotation motors may also be employed in substrate markingemploying lasers, or laser marking, of for example, semiconductors,wafers and the like on either front or backsides of the substrates. Themarks produced by the laser (such as a diode pumped solid state laser),whether on a front or back side, may be formed as a ID or 2D matrix, andin compliance with various industry standards. The performance of such asystem may depend, at least in part, on marking speed, density, andquality, and improvements in limited rotation motor performance mayimprove marking speed, density and quality. Marking speed over a field,as measured in mm/sec for example, is a function of the laser repetitionrate, spot size, and the speeds of the one or motors (e.g., low and fastscan direction motors) used in the system.

In accordance with further embodiments, systems of the invention may beprovided for other high speed marking applications in the electronicindustry such as, for example, marking of packages or devices in trays,or other similar workpieces.

Limited rotation motors as discussed above may also be employed in lasertrimming systems in accordance with further embodiments of theinvention. One or more embodiments of the present invention may be usedin a laser trimming system, or in a substrate micromachining system. Forexample, such a system may provide a method for high-speed, precisemicromachining an array of devices (such as resistors), which each ofthe devices having at least one measurable property (such asresistance). The method includes the steps of: a) selectivelymicromachining device in the array to vary a value of a measurableproperty; b) suspending the step of selectively micromachining; c) whilethe step of selectively micromachining is suspended, selectivelymicromachining at least one other device in the array to vary a value ofa measurable property; and d) resuming the suspended step of selectivelymicromachining to vary a measurable property of the device until itsvalue is within a desired range. At least one of the steps ofselectively micromachining may include the steps of generating andrelatively positioning a laser beam to travel in a first scanningpattern across the devices, superimposing a second scanning pattern withthe first scanning pattern and irradiating at least one device with atleast one laser pulse.

A micromachining system in accordance with another embodiment of theinvention may provide for a fast scan pattern to be carried out usingwith an acousto-optic deflector, superimposed on a second, lower speedscan pattern that is carried out using a limited rotation motor asdiscussed above. Generally, the access or retrace time of theacousto-optic deflector is on the order of tens of microseconds. Incertain embodiments improved motor speed will directly result inimproved trimming speed.

Those skilled in the art will appreciate that numerous modifications andvariations may be made to the above disclosed embodiments withoutdeparting from the spirit and scope of the invention.

1-31. (canceled)
 32. A scanning assembly for providing controlledmovement of a mirror, said scanning assembly comprising a motor shaft ofa limited rotation motor, a scanning device, and a scanning devicemounting unit, said mirror mounting unit comprising a tapered base forcoupling the scanning device mounting unit to the output shaft of thelimited rotation motor, one of said tapered base and the output shaftincluding a cylindrical tapered male plug having a decreasing innerdiameter that decreases along a direction of coupling of the taperedbase and the output shaft for engaging the tapered base to the outputshaft, said tapered base including an overall taper angle of at mostabout 4.0 degrees from the rotational axis of the output shaft.
 33. Thescanning assembly as claimed in claim 32, wherein said tapered base is atapered male plug for engaging a female end of the output shaft.
 34. Thescanning assembly as claimed in claim 32, wherein said tapered base is atapered female end for engaging a male end of the output shaft.
 35. Thescanning assembly as claimed in claim 32, wherein said tapered baseincludes a taper angle of between about 1.7 degrees from the rotationalaxis of the output shaft to about 4.0 degrees from the longitudinal axisof the output shaft.
 36. The scanning assembly as claimed in claim 32,wherein said tapered base is formed of a material that is different thana material of the output shaft.
 37. The scanning assembly as claimed inclaim 32, wherein the mirror is cemented into a slotted opening in saidmirror mounting unit.
 38. The scanning assembly as claimed in claim 32,wherein a taper angle on the tapered base and an engagement length areselected such that an interface between the base and the output shaftforms a permanent lock.
 39. The scanning assembly as claimed in claim32, wherein a taper angle on the tapered base and an engagement lengthare selected such that an interface between the base and the outputshaft forms a non-permanent engagement of the plug and the output shaft.40. The scanning assembly as claimed in claim 32, wherein the taperedbase is bonded to the output shaft.
 41. The scanning assembly as claimedin claim 32, wherein said scanning device mounting unit is formed of anyof silicon carbide, titanium, and beryllium.
 42. The scanning assemblyas claimed in claim 32, wherein said scanning device is coupled to saidscanning device mounting unit via a receiving means for receiving saidscanning device on said scanning device mounting unit.
 43. The scanningassembly as claimed in claim 32, wherein said scanning device isintegrally formed with said scanning device mounting unit as a unitarystructure.
 44. The scanning assembly as claimed in claim 32, whereinsaid tapered base includes a taper that is linear.
 45. The scanningassembly as claimed in claim 32, wherein said scanning assembly isprovided in a laser drilling system.
 46. The scanning assembly asclaimed in claim 32, wherein said scanning assembly is provided in alaser marking system.
 47. The scanning assembly as claimed in claim 32,wherein said scanning assembly is provided in a substrate machiningsystem.
 48. The scanning assembly as claimed in claim 32, wherein saidscanning assembly is provided in a laser trimming system.
 49. A scanningassembly for providing controlled movement of a mirror, said scanningassembly comprising a motor shaft of a limited rotation motor, ascanning device, and a scanning device mounting unit, said mirrormounting unit comprising a tapered base for coupling the scanning devicemounting unit to the output shaft of the limited rotation motor, one ofsaid tapered base and the output shaft including a tapered male plughaving a decreasing inner dimension that decreases along a direction ofcoupling of the tapered base and the output shaft for engaging thetapered base to the output shaft, said tapered base including a taperangle of between about 1.7 degrees and about 4.0 degrees from therotational axis of the output shaft.
 50. The scanning assembly asclaimed in claim 49, wherein no adhesive is required to maintain contactbetween the tapered base and the output shaft during assembly, yetre-adjustment of the angular position of the shaft during assembly andalignment of the mirror mounting unit is permitted.
 51. A scanningassembly for providing controlled movement of a mirror, said scanningassembly comprising a motor shaft of a limited rotation motor, ascanning device, and a scanning device mounting unit, said mirrormounting unit comprising a tapered base for coupling the scanning devicemounting unit to the output shaft of the limited rotation motor, one ofsaid tapered base and the output shaft including a tapered male plughaving a decreasing inner dimension that decreases along a direction ofcoupling of the tapered base and the output shaft for engaging thetapered base to the output shaft, said tapered base including an overalltaper angle of at most about 4.0 degrees from the rotational axis of theoutput shaft, and said scanning device mounting unit being formed of anyof silicon carbide, titanium, and beryllium.